Stainless Steel Bellows Stop Valve: Failure Analysis and Solutions
I. Failure Cause Analysis
Leakage in bellows stop valves can be categorized into internal leakage and external leakage. Internal leakage is typically caused by solid impurities in the medium damaging the sealing surface. Based on on-site analysis, external leakage is primarily attributed to three factors: structural design, working environment, and operation method.The main stop valve product names of China Stop Valve Network include:Bellows Globe Valve,Valve Stem Leakage,Marine Power Plant Piping,Corrosion Seizure,External Leakage,Dual Sealing Structure,Failure Analysis,Valve Operation.
1. Structural Design
The valve features a dual sealing structure combining bellows and packing. The bellows assembly is welded to the valve stem and guide body to prevent medium leakage. When the valve stem is over-opened, flat key I moves upward until it contacts the PTFE lower packing. Excessive opening may cause flat key I to embed into the soft PTFE material, leading to valve jamming, bellows damage, and subsequent external leakage. Therefore, limiting devices must be installed to ensure the bellows operates within its designed extension and compression range.
2. Working Environment
Valves installed in marine environments are exposed to persistent salt spray and condensation. Dripping condensate often causes corrosion of the thrust ball bearing and, in severe cases, leads to contact corrosion of the valve stem.
3. Operation Method
Over-closing the valve may damage the sealing surface, resulting in internal leakage. Over-opening may damage the bellows assembly, causing external leakage. Proper operational techniques are essential to prevent these failures.
II. Improvement Measures
Based on the analysis, the following improvements were implemented:
Structural Enhancement: Added a limiting function for flat key I and installed a 3mm thick stainless steel packing seat beneath the PTFE lower packing to prevent packing deformation and provide effective valve stem limiting.
Operational Guidelines: When the valve fails to seal during closing, avoid forced closure. Instead, open the valve to flush the sealing surface with fluid before attempting to close again. If the issue persists, inspect and grind the sealing surface. During opening, stop when slight resistance is encountered to extend the service life of the bellows and sealing components.
Environmental Protection: For valves equipped with thrust ball bearings, ensure installation prevents condensate from dripping directly onto the valve stem and bearing areas to minimize corrosion.
III. Conclusion
Following these improvements, the bellows globe valve has experienced no further failures such as bellows rupture, valve stem corrosion seizure, or external leakage. The valve now operates stably and reliably, demonstrating the effectiveness of the implemented solutions.
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